Looking at the trends in the construction of composite components, it can be observed that the fiber-reinforcements are used selectively local where they are necessary. An efficient and also cost-effective lightweight construction is possible by the local use of the reinforcements. By the local use of fiber-reinforcements, leaps of the wall thickness are occurring frequently in the semi-finished product.
In order to mention a method which produces such semi-finished products selectively adjusted to the component, for example tape-laying of thermoplastic tapes has to be quoted. Here, tapes of different lengths, widths and orientations—which can also be fiber-reinforced—are placed down onto each other in order to selectively modify the mechanical characteristics. By the selective modification, leaps of the wall thickness cannot be avoided oftentimes.
There are different approaches in the different tape laying methods how such tapes are attached on each other. On the one hand, there are methods which connect the tapes holohedral and, thus, do not need subsequent consolidation of the semi-finished products. On the other hand, there are methods which partially weld or stick together the tapes and, thus, necessitate a subsequent consolidation.
For consolidation of such semi-finished products, double-belt presses are currently primarily used. Looking at the double-belt presses more precisely, three design variants for the consolidation of thermoplastic composites can be named. On the one hand, there are double-belt presses which use PTFE foils for transporting the semi-finished products. PTFE foils, however, only allow low pressures and low temperatures.
Further, there are also double-belt presses which use metallic strips for supporting the semi-finished products. With these metallic strips, higher temperatures and also higher pressures are possible. Such double-belt presses work continuously. The semi-finished product is inserted and passes a certain heating line till it reaches consolidation temperature. As soon as this temperature is reached, consolidation pressure is exerted onto the semi-finished product in order to connect the single layers with each other. Subsequently, the semi-finished product is again cooled in the cooling line and can subsequently be removed from the press.
There are also double-belt presses which work discontinuously. There, the semi-finished product is laid onto a conveyor belt and subsequently heated in a first press to a consolidation temperature, transported into the cooling press via the conveyor belt, and finally pressed and cooled under a specific consolidation pressure.
Both of these systems are working very well as long as it concerns flat semi-finished products. If, however, having a semi-finished product with several wall thicknesses, a consolidation with such press systems is considerably more complex. In order to produce semi-finished products with several thicknesses, matrices have to be used which compensate these leaps of the wall thicknesses. Thus, it is possible to produce semi-finished products with different wall thicknesses. However, the process is losing economic efficiency, because the matrices have to be additionally placed again and again on the semi-finished products.